182 ELEMENTARY PHYSIOLOGY. [XVII. 



divisions varies greatly in different animals, there 

 is also considerable variation in the form of the 

 tubes and in the appearance of the cells in diffe- 

 rent animals, generally speaking the cells are 

 much the same in the ducts and throughout the 

 tubes ; the nuclei are placed near the basement 

 membrane. 



5. Prepare vertical transverse sections of the large 

 intestine. Observe 



a. The longitudinal muscular coat, thin except 

 where the section has passed through one of 

 the three conspicuous bands. 



6. The circular coat, thick and well developed. 



c. The mucous membrane, frequently thrown 

 into longitudinal ridges, the sub-mucous tissue 

 running up into the ridges. 



cZ. The absence of villL 



c. The intestinal glands (glands of Lieberkiihn) ; 

 they are larger than in the small intestine, 

 and their features, owing to the absence of 

 villi, much more easily seen. The epithelium 

 covering the free intestinal surface or the 

 ridges between the glands consists of long 

 columnar cells with usually a striated clear 

 free border, in the glands the cells are 

 shorter, have no clear border, and the nuclei 

 are nearer the basement membrane ; in some 

 animals (e.g. dog) there are many distinct 

 goblet cells. 



